Piezoelectric vibrator



Aug. 6, 1946. BENIOFF 2,405,186

PIEZOELEC'IRIG VIBRATOR Filed Oct. 8, 1941 INVENTOR Patented Aug. 6,1946 FFEC PIEZOELECTBIC VIBRATOR Hugo Beniofl", La. Canada, Calif.,assignor to Submarine Signal Company, Boston, Mass, a

corporation of Maine Application October s, 1941, Serial No. 414,132

11 Claims.

The present invention relates to a piezoelectric vibrator of the generaltype described and claimed in my copending applications Serial Nos.386,583, filed April 3, 1941, and 344,363, filed July 8, 1940. closed avibrating unit in which th piezoelectric crystals are secured tochannels or recesses in the side walls of the vibrating unit, the unititself forming a vibrating element in which the end acts as a acousticradiating face. Where the unit is attached to a diaphragm, the diaphragmforms a part of the section of the unit. One of the limita tionsencountered in the operation of devices employing piezoelectric crystalsis that the crystals are limited in their power-handling capacity andwhile these factors are not detrimental when the devices are acting asreceivers, however, they may seriously interfere with th utility ofpiezoelectric crystals in their use for transmitting increased acousticpower.

In the present invention a plurality of vibrators are used in which theindividual vibrating units have a plurality of nodes and loopscorresponding in efiect to a vibratory system of two or more wavelengths. In these units the crystals are mounted in recesses at th sidesof th units and are cut and mounted such that the polarities ofsuccessive crystals provide expansion and contraction nodes in thecorresponding crystals alternately longitudinally along the vibratorystructure. This action is reciprocal inasmuch as the expansion andcontraction along the vibratory structure generate potentials across thecrystal electrodes which cooperate together in the electrical circuit.Various specific means may be employed to accomplish this result. In onecase the crystals may be arranged so that the potentials generated byalternate crystals under contraction and expansion produce the samepotential on all the exposed electrodes of the vibrator and similarlythe same but opposite potential on all the unexposed or groundedelectrodes of the vibrator, each group being opposite in potential tothe other group at an instant. In another arrangement the crystals mayhave a parallel series connection, in which case successive crystalshave their external electrodes alternately poled. In the latter case thimpedance will be four times the impedance of the first case and willunder certain conditions not be as preferable as the first-mentionedarrangement.

By the use of either of these arrangements the driving forces may beapplied at many points along the vibrator, thus substantially reducingthe power which each individual crystal needs to In each of theseapplications there is discarry. Due to the fact that the damping lossesof the sound or mechanical wave in metal is very slight and that byproper choice of the mass elements in the system the amplitudesefiective upon the crystals may be accurately chosen, it i possible todesign the longitudinal vibrator members in such a manner that all thecrystals operate synchronously for transmission and reception withoutexceeding in any way the power which the crystal is capable of handling.

In the piezoelectric harmonic vibrator of the present design it has beenpossible by these expedients to obtain from the impressed electricalenergy to th sound energy transmitted to the water an overall efficiencyof approximately at frequencies well within the supersonic range. Theso-called harmonic vibrator of the present invention may be nestedtogether for projecting a beam of compressional wave energy and fordirectively receiving compressional wave energy in the Water or othermedium. The harmonic vibrator may, however, also be used as a linearstructure in which one or more long vibratory elements may be usedindependently or together. These long vibratory structures may have alength of twelve or more wav lengths and may be used under variouscircumstances for directive or partially directive transmission andreception.

Various further objects and advantages of the present invention will beunderstood from the description given in the specification below inconnection with the illustrations in the drawing showing an embodimentof the invention in which Fig. 1 is a sectional view of the inventiontaken longitudinally through the vibrating elements on the line ll ofFig. 2; Fig. 2 is a sectional view taken on the line 22 of Fig. 1; Fig.3 shows a modification of the form of oscillator used in Fig. 1 in whichthe vibrator units are double the length shown in Fig. 1; Fig. 4 shows afragmentary section taken on the line i4 of Fig. 3; Fig. 5 shows an endview of one of th vibrating units; Fig. 6 shows a detail of aninsulating support in perspective; Fig. 7 shows the same detail inelevation; Figs. 8 and 9 show circuit connections for the crystalelements of the vibrator; Fig. 10 shows one of the oscillating units ina longitudinal view partly in section; and Fig. 11 shows a horizontalsection taken on the view of Fig. 10.

In the arrangement indicated in Figs. 1 and 2 there are provided anumber of longitudinal vibrators I, l, I, etc., which are mounted on adiaphragm or plate 2 which is exposed to the compressional Wave orsound-propagating medium which may be air, water or other medium, theil- 3 lustration in Figs. 1 and 2 being more particularly adaptable fora liquid medium. As indicated more clearly in Fig. 2 the vibrators I, l,I, etc., may be nested together oVer substantially the whole surface ofthe plate 2, thus applying the vibrations of the longitudinal vibratorssimultaneously over the Whole area of the plate. The plate 2 is providedwith a thin peripheral flange 3 supporting the plate 2 to the casing,flange or wall 4. The wall or flange 4 may be joined in any suitablemanner to the supporting casing 5 which, in turn, is supported by aplate 6 for mounting to any desired structure.

As indicated in Figs. 1 and 2 the longitudinal units I are positionedbetween shoulders I, I, 1, projecting slightly from the rear of theplate 2. These shoulders act to locate accurately the vibrating unitsand to space them slightly apart from each other. The Vibrating unitsare each cemented to the plate 2 and also bolted and screwed down bymeans of the screw 8 which is located in the longitudinal hole 9 andextends through the base of the vibrator into the plate 2. Each screwhead is provided with a suitable flange so that the vibrator is securelyheld in place.

Referring to Fig. l, the crystal elements I0, [2 and I3 are of thepiezoelectric type, preferably Rochelle-salt crystals or crystals havingsimilar piezoelectric action. These crystals are so cut that compressionon the upper and lower end surfaces produces electrical potentialsacross the crystal electrodes the inner ones l4 |5, |6 and I! of whichare grounded to the metal of the longitudinal vibrating bar or elementThe outer electrodes |8,- I9, 20 and 2|, on the other hand, may all havethe same potential when excited oppositely or they may be so faced thatdistance between successive crystal edges, as,

the potential of the group of the pair l8 and I9 is opposite to that ofthe pair 20 and 2| as illustrated by the circuit arrangement of Figs. 8and 9. The electrodes of the exposed surfaces of the crystals, that is,the outer electrodes, are connected by means of a conductive ribbon 22which may be an extension of the electrodes to the bus wire 23. Theribbon 22 extends around the sides of the crystals through a channel 24which is cut out of the metal of the vibrating unit. This channel 24joins the verticalchannel 25 in which the bus wire 23 is positioned.

The bus wire 23 is supported away from the channel by an insulatingbridge which is shown in Figs. 6 and 7 and in section in Fig. 10. Thisinsulating bridge or support for the wire 23 comprises an insulatingpiece 26 made of a suitable product, such as that known by the tradename Bakelite, and which has a cross section in the form of a ratherflat C, the bus wire 23 passing through the end elements of the C andsupporting the wire away from the sides and base of the channel. Theinternal electrodes l4, Hi, It and I1 are grounded to the metal of thevibrating unit by leading the conducting ribbon which may form a part ofthe inner electrode over a channel 21 similar to the channel 24 andjoining the end 28 of this conducting ribbon to a terminal connection 29positioned in the vertical channel 30 corresponding to the channel 25but on the opposite side of the vibrating unit, as indicated clearly inFig. 10. Each external electrode is connected to a vertical bus wire 23and all of these, in the construction shown in Fig. 1, are joined andelectrically connected to the bus bar 30' which is supported at eitherend to insulating brackets or supports 3| and 32 attached to the insideof the casing.

for instance, B, B, and, further, that the distance between the top ofthe vibrating unit 0 and the top edge of the crystal unit C is equal tothe distance between the edge A and the external water surface oftheplate 2. The vibrating unit by these means is made of a type which mightbe called a true harmonic vibrator inasmuch as the external watersurface and the internal boundary of the vibrating unit with the airmedium have substantially the same amplitude as the maximum amplitudebetween the points 13 and B neglecting, of course, the slight differencethat occurs because of energy radiation or radiation resistance which,at the high frequencies here considered, hardly affects in any way theuniformity of the vibrating element. By making larger recesses for thecrystals and consequently increasing the metal masses in the sectionsbetween crystals as compared to the inass of metal where the crystalsare placed, the

vibrating element becomes loaded and this load- .ing may be soproportioned that maximum permissible vibrational amplitude is obtained.In using units such as just described for projecting sound beams issubaqueous media, it is essential .to maintain the working of thecrystal units well within their operating capacity, since heating of thecrystal elements soon brings about a loss of efficiency and, in fact,considerable danger from possibility of destruction or burning up of thecrystals. This is particularly true. with the use of Rochelle-saltcrystals.

In the arrangements indicated in Figs. 1 and 2 the vibrating units areof the type which may be called a whole wave-length vibrator. In thiscase the lower set of units and the upper set of units are always 180degree out of phase with each other, one set contracting while the otherset isexpanding. In this arrangement all the acoustic radiation isproduced by the external surface of the plate 2 in contact with theliquidpropagating medium. The other free ends of the vibrating unit aresealed off from the liquid medium by means of the casing 5 and the coverplate 33. Where longer units are to be used as, for instance, in thearrangement indicated in Figs. 3 and 4, it is desirable to support bothends of the vibrating unit in the same manner. In

' the arrangement indicated in Fig. 3 the plate 40 has its externalsurface in contact with the radiating medium. On the plate 40 is nesteda group of vibrators in a fashion similar to that indicated in Figs. 1and 2. The plate 40 is bounded by a supporting thin flange 4| whichmerges into a heavy peripheral supporting member 42 formed as a shellabout the vibrating units and radiating member. This shell 42 extendsbackwards into the wall 43 which has formed with it an outwardlyextending flange 44. Attached to the other end of the vibrating units46, in which the piezoelectric crystals 45 are placed similarly as H inFig. 1, is a plate 4! which has the same thickness and is of the samegeneral construction as the plate 49. The plate 40 is provided withseparating ribs 48 andsimilarly the plate 41 is provided with the samekind of separating ribs 49. The plate 41 is also supported by the flange50 of the same construction and thickness as the flange 4i, and thisflange 50 merges into a supporting peripheral member 5| which extendsbackwards into the shell 52 meeting the outwardly extending flange 44 inthe section 53 at the end of the shell 52. The flanges 53 and 44 come inface-to-face contact with each other and are bolted together to supportthe vibrators at a point midway between their ends. A cover or casing 55may be placed on ithe back end of the unit Where it is desired that theunit shall radiate only from the forward end as, for instance, the platemember 49. To provide electrical connections for the electrodes theplate member 4? i perforated at spaced intervals with holes 56 to whichthe vertically extending bus wires 5'! connecting the externalelectrodes are projected. These bus wires 51 are electrically connectedto a cross bus wire 58 to which all of the vertically extending buswires 51 are joined. The insulating supporting member 59 is of the sametype as described in Figs. 6 and 7, and supports the electricalconnections free from the metal of the vibrating units.

In the assembly of the system the units 46 are cemented to the radiatingplate members 40 and boltedin place by means of screws 60 which may beproperly adjusted through the hollow channel 6! in each unit. At the topof the vibrating unit there is provided near diagonal corners twothreaded taps 62 and 63 and the screws 64 and 65 screwed into theseholes through the plate 41. The unit should also be cemented in thesejoints to the plate 41 as well as in the joint to the plate 4!). Inorder to establish the units as balanced harmonic vibrators the distancefrom the outer surface of the back plate 41 to the edge of the nearestcrystal is half the distance between successive crystals and is equal tothe distance between the water surface and the end of the nearestcrystal.

The vibrating unit, when operating as a harmonic vibrator, has thecrystals positioned successively along the vibrator operating inopposite phases so that when one crysta1 is experiencing an expansionnode, the crystal next in line F is experiencing a contracting node. Inorder that the crystals should cooperate in this arrangernent they mustbe correctly poled. This may be accomplished either by the arrangementindicated in Fig. 8 or that indicated in Fig. 9. i

In the arrangement of Fig. 8, which may be applied to the vibratory unitof Fig. 1, in which there are two pairs of crystals in line, the onepair of crystals 6! and 62 may have their external electrodes 53 and 64energized from one terminal 66 of the oscillating source 55, the innerelectrodes 61 and 68 being connected to ground which is the vibratorybody itself. The inner electrodes 69 and. 10 of the other pair ofcrystals H and 12 are likewise grounded to the vibratory unit while theexternal electrodes 13 and 14 are connected to the other terminal 16 ofthe oscillator 65'. In efiect this may be called a series parallelconnection with the crystals BI and. 62 being connected in parallel aswel1 also as the crystals H and l2,v the two pairs being connected inseries with the oscillating source. In this arrangement in Fig. 8 itwill be noted that when the potentials on. the electrodes 63' and 64 arepositive that the potentials on the electrodes 13 and M are negative,and that this condition in the next half cycle of the oscillator 65 isreversed. This arrangement, however, will permit one group to operateunder a contraction node while the next group is operating under anexpansion node, and vice versa. Where eight crystals are used, twoalternate pairs will have the external electrodes connected to oneterminal of the oscillator and the two other pairs will have theexternal electrodes connected to the other terminal of the oscillator.

In the arrangement indicated in Fig. 9 the crystals are all excited in asimilar fashion. In this case the oscillator'B5 has one terminalconnected to the external electrodes of each crystal iii, 82, 83 and 34while the internal electrodes are all grounded, the ground being theother terminal of the oscillator 85. Since in the arrangement of Fig. 9the potentials will all be simultaneously impressed in the same phase onall the exter nal electrodes, the same result may be accomplished ofoperating the crystals with expansion and contracting nodes insuccessive crystals along the vibrator by orienting the crystals 8| and82 opposite from that of 83 and 84. In other words, the crystal 8| willbe so oriented as regards 83 that when the external electrodes of 81 and83 are positive, the crystal 8| will be under an expansion node and 83under a contraction node, or vice versa, and when the potentials change,the reverse effect will obtain. The orientation is simply accomplishedby using as the external electrodes alternately opposite crystal facesof the crystal, or, in other words, simply reversing the crystal.

The arrangement of the circuit of Fig. 9 may at times be preferable tothat of Fig. 8 since it will be evident from the circuit that thearrangement of Fig. 8 has four times the impedance of that of Fig. 9.

Having now described my invention, I claim:

1. A piezoelectric oscillator for the production and reception ofcompressional Waves comprising a radiating plate having mounted thereona plurality of longitudinal vibrating elements substantially coveringsaid radiating plate. said longitudinal vibrating elements each havingmounted in recesses in the sides thereof a plurality of piezoelectriccrystals. said elements together with the crystals and the radiatingplate forming a harmonic vibrator in which successive crystals along thevibrator at any instant of operation are vibrating in opposite phase andall crystals nearest the plate, for piston operation of the plate, arevibrating in the same instantaneous phase. and electrodes attached tosaid piezoelectric crystals providing the desired instantaneous polarityto the crystals according to its instantaneous phase of vibration.

2. A piezoelectric oscillator for the production and reception ofcompressional waves comprising a longitudinal vibrating element havingmounted in the sides thereof a plurality of piezoelectric crystals, saidelement together with said crystals forming a harmonic vibrator in whichsuccessive crystals along the vibrator at any instant of operation arevibrating in opposite phase, and electrodes attached to saidpiezoelectric crystals providing the desired instantaneous polarity tothe crystals according to its instantaneous phase of vibration.

3. A piezoelectric oscillator for the production and reception ofcompressional waves comprising a radiating plate having mounted in rowsthereon a. plurality of longitudinal vibrating elements,

said plate having on the inner side thereof a plurality of smallprojecting ribs spacing said rows of vibrators from each other, saidlongitudinal vibrating elements having mounted in recesses in the sidesthereof a plurality of piezoelectric crystals, said elements togetherwith said crystals and the radiating plate forming a harmonic vibratorin which successive crystals along the vibrator at any instant ofoperation are vibrating in opposite phase, and electrodes attached tosaid piezoelectric crystals providing the desired instantaneous polarityto th crystals according to its instantaneous phase of vibration. g

4. A piezoelectric oscillator for the production and reception ofcompressional waves comprising a radiating plate having mounted thereona plurality of longitudinal vibrating elements substantially coveringsaid radiating plate, said longitudinal vibrating elements each havingmounted in recesses in the sides thereof a plurality of piezoelectriccrystals, said elements together with the crystals and the radiatingplate forming a harmonic vibrator in which successive crystals along thevibrator at any instant of operation are vibrating in opposite phase,and electrodes attached to said piezoelectric crystals providing thedesired instantaneous polarity to the crystals according to itsinstantaneous phase of vibration, the spacing between the radiatingsurface of said radiating plate and the end of the nearest crystal beingequal to one-half the distance along the longitudinal vibrating elementbetween successive crystals.

5. A piezoelectric oscillator for the production and reception ofcompressional Waves comprising a radiating plate having mounted thereona plurality of longitudinal vibrating elements substantially coveringsaid radiating plate, said Ion gitudinal vibrating elements each havingmounted in recesses in the sides thereof a plurality of piezoelectriccrystals, said elements together with the crystals and the radiatingplate forming a harmonic vibrator in which successive crystals along thevibrator at any instant of operation are vibrating in opposite phase,and electrodes attached to said piezoelectric crystals providing thedesired instantaneous polarity to the crystals according to itsinstantaneous phase of vibration, the spacing between the radiatingsurface of said radiating plate and the end of the nearest crystal beingequal to one half the distance along the longitudinal vibrating elementbetween successive crystals and the distance between the end of anyvibrating element and the nearest crystal is also equal to one-half thedistance between successive crystals along the longitudinal vibratingelement.-

6. A piezoelectric oscillator for the production and reception ofcompressional waves comprising a radiating plate having mounted thereona plurality of longitudinal vibrating elements substantially coveringsaid radiating plate, said longitudinal vibrating elements each havingmounted in recesses in the sides thereof a plurality of piezoelectric,crystals, said elements together with the crystals and the radiatingplate forming a harmonic vibrator in which successive crystals along thevibrator at any instant of operation are vibrating in opposite phase,electrodes attached to said piezoelectric crystals providing the desiredinstantaneous polarity to the crystals according to its instantaneousphase of vibration, the external electrodes having conductive elementsextending in channels to the sides of said longitudinal vibratingelements and conductive bus elements positioned in channels at the'along the'vibrator at any instant of operation are vibrating in oppositephase, electrodes attached to said piezoelectric crystals providing thedesired instantaneous polarity to the crystals-according to itsinstantaneous phase of vibration, and a non-radiating plate element towhich the other ends of said longitudinal vibrating elements areattached, said plate element being of the same thickness as saidradiating plate and means for supporting the same in a plane mid waybetween the ends of the vibrator.

8. Apiezoelectric oscillator for. the production and reception ofcompressional waves comprising a radiating plate having mounted thereona plurality of longitudinal vibrating elements substantially coveringsaid radiating plate, said longitudinal vibrating elements each havingmounted in recesses in the sidesthereof a plurality ofpiezoelectriccrystals, said elements together with the crystals and theradiating plate forming a harmonic vibrator in which successive crystalsalong the vibrator at any instant of operation are vibrating in oppositephase, electrodes attached to said piezoelectric crystals providing thedesired instantaneous polarity to the crystals according to itsinstantaneous phase of vibration, and a non-radiating plate element towhich the other ends of said longitudinal vibrating elements areattached, said plate element being of the same thickness as saidradiating plate and means for supporting said plate.

9. A piezoelectric oscillator for the production and reception ofcompressional waves comprising a radiating plate having mounted thereona plurality of longitudinal vibrating elements substantially coveringsaid radiating plate, said longitudinal vibrating elements each havingmounted in recesses in the sides thereof a plurality of piezoelectriccrystals, said elements together with the crystals and the radiatingplate forming a harmonic vibrator in which successive crystals along thevibrator at any instant of operation are vibrating in opposite phase,electrodes attached to said piezoelectric crystals providing the desiredinstantaneous polarity to the crystals according t its instantaneousphase of vibration, a non-radiating plate element to which the otherends of said longitudinal vibrating elements are attached, said plateelement being of the same thickness as said radiating plate, means forsupporting said plate, and a cover spaced away from and. covering saidplate element and separating said plate element from the compressionalwave propagating medium.

10. A piezoelectric oscillator for the production and reception ofcompressional waves comprising a radiating plate having mounted thereona plurality of longitudinal vibrating elements substantially coveringsaid radiating plate, said 1ongitudinal vibrating elements havingmounted in recesses formed in two opposite sides only of said vibratorpiezoelectric crystals, said .elements together with said crystals andsaid radiating plate forming a harmonic vibrator in which successivecrystals along the vibrator at any instant of operation are vibrating inopposite phase, electrodes attached to said piezoelectric crystals, onegroup of said electrodes being in face-to-face contact with saidlongitudinal vibrating element and making electrical contact therewith,the other external electrodes of said crystals having means connectingthe same to a bus conductor, said bus conductor being mounted in achannel in the side of said longitudinal vibrating element adjacent theside in which said crystals are mounted.

11. A piezoelectric oscillator for the production and reception ofcompressional waves comprising a longitudinal vibrating element having aradiat- 10 ing face at one end, said longitudinal vibrating elementhaving uniformly spaced recesses formed in the sides thereof,piezoelectric crystals mounted in said recesses and having electrodes onopposite faces thereof, one of which substantially abuts the innerlongitudinal wall of said recess and the other being external thereto,said longitudinal vibrating element together with the crystals forming aharmonic vibrator in which successive crystals along the vibrator at anyinstant of operation are vibrating in opposite phase, and electrodesattached to said piezoelectric crystals providing the desiredinstantaneous polarity to the crystals according to its instantaneousphase of vibration.

HUGO BENIOFF.

